This invention relates generally to an apparatus for accurately determining the weight of the payload carried by a mobile machine, and more particularly, to an apparatus and method configured to determine a payload weight supported by a suspension strut located on the mobile machine.
In the field in which off-highway trucks are used, for example in mining operations, it is desirable to determine the payload weight accurately. Accurate payload weight measurements are desired for several reasons including: avoidance of overloading and truck health reasons, site productivity management and fleet productivity management. It is also desirable to generate payload weight information quickly so that the loading tool operator can gauge the density of the material being loaded and then the loading technique to avoid underloading or overloading the next truck in the queue.
Some previous systems determine the payload weight while the machine is under the loading tool, before the machine has begun moving. This technique is poorly suited to machines that use the truck suspension system as a payload measurement system because loading floors tend to be uneven, suspension struts tend to stick under static conditions and shovel operators are prone to patting the load in the bed of the truck which causes the payload system to measure the loading tool as well as the material.
Once the truck moves away from the shovel, the conditions change drastically: the coefficient of static friction is replaced with the much smaller coefficient of dynamic friction in the struts, the haul roads tend to be much more even than the loading floor, and the truck is out of reach of the loading tool so only the payload is measured. One system disclosed in U.S. Pat. No. 45,182,712 to Kyrtsos, discloses determining the payload weight while the machine is in motion and after a significant compression condition of the strut is detected. That is, the weight is determined after the machine has begun moving and then encounters a discontinuity in the road""s surface such as a pothole or bump to ensure that the struts are moving freely. Therefore the Kyrtsos system is dependent upon encountering a bump severe enough to cause a compression condition. However, a compression condition of this nature, may or may not occur during machine travel. In addition, depending on the dynamic forces associated with the machine, the payload weight is desirably determined prior to and independent of encountering a bump. Therefore, there are disadvantages associated with monitoring for an environmentally controlled triggering event that may or may not occur, before determining a payload weight.
In addition, there are dynamic forces acting upon/within the machine that affect the strut pressures of the machine. For example, a torque reaction, or torque windup, in the drive train can cause strut compression in the truck suspension system while the truck is moving. This strut compression is then seen by a payload measurement system as additional load, causing inaccuracy in the payload measurement. The dynamic forces effecting strut pressures, such as torque reaction, are desirably minimized before the payload weight is determined.
The present system is directed at overcoming one or more of the problems set forth above.
In one aspect of the present invention, a method for determining the weight of a payload loaded onto a mobile machine is disclosed. The mobile machine has a plurality of hydraulic struts in supporting relation to the payload. The method comprises the steps of establishing a force characteristic indicative of a dynamic force associated with the machine, establishing an internal pressure of at least one of the payload support struts, and determining the payload weight in response to the force characteristic, and the established strut pressure.
In another aspect of the present invention, an apparatus configured to determine the weight of a payload loaded onto a mobile machine is disclosed. The machine has a plurality of hydraulic struts in supporting relation to the payload. The apparatus comprises at least one of sensing device configured to sense an internal pressure of one of the struts, and responsively generate a pressure signal, a second sensing device configured to sense a parameter indicative of a dynamic force of the machine, and responsively generate a force characteristic signal, a controller is configured to receive the pressure signals and the force indicative signal, and determine the payload weight in response to said force characteristic, the machine being in motion, and the sensed strut pressure.